Field of the Invention
The present invention relates to an image capturing apparatus, a control method thereof, a lens unit, and an image capturing system, and particularly to control at a time of focus adjustment.
Description of the Related Art
In recent years, due to digitization of single-lens reflex cameras, single-lens reflex digital cameras that are capable of performing live-view shooting and moving image shooting as well as still image shooting have become common. Generally, the auto-focus (AF) method used in a single-lens reflex digital camera is different in the case of still image shooting and in the case of moving image shooting or live-view shooting that allows the user to check the subject on the liquid crystal monitor of the camera while shooting an image.
Japanese Patent Laid-Open No. 2010-197646, for example, discloses a lens control system for an interchangeable-lens cameras, as follows: first, during still image shooting, a portion of the light flux of the subject image entering via an imaging lens is reflected toward an AF sensor by a sub mirror inserted in the light path, and thus a pair of image signals are generated by the AF sensor. A camera CPU calculates a defocus value based on the phase difference between the pair of image signals, and drives a focus lens by communicating with a lens unit according to the result of the calculation, thereby focusing on the subject.
During moving image shooting or live-view shooting, a main mirror (instant-return mirror) and the sub mirror are flipped up and are thereby withdrawn from the light path so that the subject image entering via the imaging lens is incident on an image sensor. An image processor calculates a contrast value and so on based on image information acquired from the image sensor, and transmits values thus calculated to the camera CPU via communication. The camera CPU performs communication with the lens unit according to the information from the image processor, and focuses on the subject.
In the conventional art disclosed in Japanese Patent Laid-Open No. 2010-197646, communication with the lens unit is always performed via the camera CPU, and the camera CPU generates information for controlling the driving of the imaging lens. For this reason, in order to transmit an instruction for controlling the driving of the focus lens to the lens unit during moving image shooting or live-view shooting, the image processor needs to transmit a contrast evaluation value used for generating information for controlling the driving of the focus lens, to the camera CPU via communication. In this way, it is necessary to perform two-step communication processing in order to transmit an instruction to drive the focus lens to the lens unit, and there is the problem that a time lag occurs due to the communication.